The use of Radio Frequency Identification (“RFID”) tags to monitor migration or biometrics of species is well known in the art. It is also well known to implant such RFID tags subcutaneously, within the musculature or within the body cavity of fish and other underwater species. Transponders suitable for implantation in fish and other underwater species necessarily have to be small, and are typically glass-encapsulated in order to be biologically inert.
Numerous types and styles of air or ferrite core antennas have been developed and used for underwater interrogation of RFID tags on fish and other underwater species. Typically such antennas include an air core antenna that is positioned flat on a substrate and deployed in a housing. The housing may be plastic pipe, or welded sheets of plastic, or similar materials and construction. Multiple wire coils may also be deployed within such a housing, typically held in position relative to each other, and as a unit, within a gallery or similar structure.
The charging and reading zone for small glass-encapsulated transponders is typically limited to distances less than 2.5 feet in the zone immediately above the antenna. Precise performance depends on factors such as the type and quality of the transceiver and antenna system, the level of ambient electromagnetic interference and the operable quality of the RFID tag itself. Some conventional air coil antennas are known to be mounted upright within the water column, perpendicular to the flow of water. Such placement has shown a tendency to increase the charging zone or read zone of transponders. Properly configured and deployed at appropriate settings, the charging zone and read zone of such antenna systems can extend to the entire water column. However, the placement of such antennas, coupled with their vertical orientation, makes these more likely to be damaged by floating debris and high water velocities in streams and rivers, especially during seasonal high water events.
Therefore, there exists a need for an improved antenna system that can read RFID tags throughout the entire water column, and yet withstand the potential physical abuse in stream or river deployments caused by high water velocity or turbulence, or by impact with moving debris or ice.